The Greenland shark, for all its exploits, does a very good job of avoiding humans.

Its meat is poisonous, and it lives only in the coldest, deepest parts of the ocean.

There, the sharks are king, at the top of the food chain. One was found with an entire reindeer, antlers and all, in its stomach.

Legend has it they can live 500 years, although, like much else about the species, that is more myth than fact.

True to form, when a Greenland shark was caught off Sable Island recently and brought to Halifax to be dissected, it proved stubborn about giving up its secrets.

“You’re talking about one of the world’s largest predators,” said Steve Campana, the scientist who performed the autopsy.

“And yet we have no idea how long it lives, or how many young it produces, or where it gives birth, how many are out there — we know nothing.”

Despite their name, Greenland sharks are very much Canadian animals, with many, maybe a majority, living in Canada’s waters, said Campana, the director of the Canadian Shark Research Laboratory at the Bedford Institute of Oceanography in Dartmouth.

He has dissected the sharks before, but never one as big as the 4.3-metre, 680-kilogram female that a fisherman delivered to his lab a week or two ago.

“He was catching halibut and this Greenland shark came along and ate one of the halibut off his line, and got hooked itself,” said Campana.

It took Steven Lyons about an hour to wrestle the shark aboard his ship. He knew how badly Campana wanted it.

The mature female, in some ways, helped answer burning questions.

“In this case, we did not see any embryos or young sharks in there,” said Campana, who had wanted to learn about the species’ gestation. “However, we could tell from the way the reproductive organs were that it had recently given birth, which was very cool.”

That suggests the sharks’ birthing season is around now, unlike two other Canadian shark species that give birth in the spring.

In other ways, Greenland sharks are uniquely puzzling, but the Sable Island female may help.

“In most sharks, the backbone, the vertebrae in the backbone, form growth rings just like a tree. We can prepare this in a special way and count those rings and figure out how old the shark is,” said Campana. “We do this routinely for all of our other shark species in Canada, and around the world, for that matter.”

But Greenland sharks’ cartilage is so soft you can poke a finger right through their backbones. Scientists have never determined the age of any specimens.

A study in 1950s Iceland came up with the 500-year estimate. It is very unlikely, said Campana, although there is no doubt the sharks get very old. He plans to use a special method to try to date the mature female’s backbone.

Greenland sharks are the number-one suspect in the mystery of what is leaving hundreds of seal corpses on the shores of Sable Island, strangely mutilated.

“It’s almost like they use their teeth to slice open the skin and they strip off the blubber layer inside, which is very high energy, and then they don’t eat the rest of it,” said Campana. However, the female’s stomach contents were unidentifiable, “like soup.”